I haven’t had any work done on the brakes so I’d assume it’s unlikely to be due to the brake fluid.
I have also had my warranty request denied due to the dealer sighting use of wheel cleaning products rather than shampoo as per the owners manual. It’s pretty ridiculous that they don’t use a more durable lacquer that can be cleaned with ph neutral and or acid free cleaners. I’ve been quite careful about the products I use so it’s disappointing.
I probably should have used some kind of sealant or ceramic coating on the callipers although I’m not convinced this would make a big difference.